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Abstract:

The present invention relates to a radiation image processing apparatus
and a processing method. A processing condition selector selects from a
processing condition memory a processing condition for extraction or
removal of a specific object in radiation image information. The
processing condition includes two different image capturing conditions
which are provided to a radiation source controller. The radiation source
controller controls a radiation source with each image capturing
condition to apply radiation to a subject and a solid-state radiation
detector stores radiation image information of the subject. An image
processor performs a weighted subtraction using stored radiation image
information in accordance with the processing condition to achieve
extraction or removal of the specific object. The resultant radiation
image information is displayed on a display unit.

Claims:

1. A radiation image processing apparatus that performs extraction or
removal of a specific object in a radiation image using a plurality of
pieces of radiation image information, each obtained by applying
radiation to a subject at different radiation energies, the apparatus
comprising:a radiation source for applying the radiation to the subject;a
radiation source controller for controlling the radiation source in
accordance with different image capturing conditions;a radiation
converting panel for receiving and converting the radiation that has
passed through the subject into radiation image information;a processing
condition memory for storing processing conditions, the processing
conditions including the image capturing conditions for extraction and
removal of the specific object;a processing condition selector for
selecting from the processing conditions in the processing condition
memory a processing condition corresponding to the target; andan image
processor for processing, in accordance with the selected processing
condition, the plurality of pieces of radiation image information
obtained from the radiation converting panel with the different image
capturing conditions.

2. The apparatus according to claim 1, wherein the image capturing
condition includes a tube voltage and a tube current for the radiation
source, the tube voltage and tube current depending on a type of the
specific object.

3. The apparatus according to claim 1, wherein the processing condition
includes a weighting coefficient for a weighted subtraction using the
plurality of pieces of radiation image information obtained from the
radiation converting panel.

4. A radiation image processing method that performs extraction or removal
of a specific object in radiation image information using a plurality of
pieces of radiation image information, each obtained by applying
radiation to a subject at different radiation energies, the method
comprising the steps of:setting a processing condition including
different image capturing conditions in order to perform extraction or
removal of the specific object;controlling a radiation source in
accordance with the different image capturing conditions, and applying
the radiation to a radiation converting panel through the subject;
andprocessing, in accordance with the processing condition, the plurality
of pieces of radiation image information obtained from the radiation
converting panel with the different image capturing conditions.

5. The method according to claim 4, wherein the image processing of the
plurality of pieces of radiation image information includes performing a
weighted subtraction using the plurality of pieces of radiation image
information obtained from the radiation converting panel, and the
processing condition includes a weighting coefficient for performing the
weighted subtraction.

6. The method according to claim 5, wherein the weighted subtraction is
computed usingS=aS1+S2 where S is a piece of resultant
radiation image information, S1 is a piece of the radiation image
information obtained with a first one of the image capturing conditions,
S2 is a piece of the radiation image information obtained with a
second one of the image capturing conditions, and α is the
weighting coefficient.

7. The method according to claim 6, wherein the first and second image
capturing conditions remain fixed, and the weighting coefficient α
varies with the specific object and the image capturing site.

8. The method according to claim 6, wherein the weighting coefficient
α remains fixed, and the first and second image capturing
conditions vary with the specific object and the image capturing site.

9. The method according to claim 5, wherein the weighted subtraction is
computed usingS=K1S1+K2S2+K3 where S is a
resultant piece of radiation image information, S1 is the piece
radiation image information obtained with a first one of the image
capturing conditions, S2 is the piece of radiation image information
obtained with a second one of the image capturing conditions, and
K1, K2 and K3 are weighting coefficients for adjusting
contrast and brightness.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to a radiation image processing
apparatus and a processing method for extraction or removal of a specific
object in a radiation image using a plurality of pieces of radiation
image information acquired by applying radiation of different energies to
a subject.

[0003]2. Description of the Related Art

[0004]In the medical field, for example, extensive use is made of
radiation image processing apparatus which expose a subject (patient) to
radiation emitted from a radiation source, guide the radiation that has
passed through the subject to a radiation converting panel for converting
radiation into radiation image information, and then perform
predetermined image processing on the radiation image information.
Processed radiation image information is displayed on a display unit and
can be used for diagnosis etc.

[0005]One example of the radiation converting panel is a solid-state
detector that converts radiation into charge information and stores the
charge information so that it can be read out as an electric signal.
Another example of the radiation converting panel is a stimulable
phosphor panel. The stimulable phosphor panel stores radiation energy in
a phosphor and emits stimulated light of an intensity corresponding to
the stored energy when irradiated with stimulating light such as a laser
beam.

[0006]One practical application of the radiation image apparatus is the
extraction of a region of interest in the subject, e.g., soft tissue such
as the heart and lungs located under ribs, from the radiation image
information. The extraction of the region of interest is achieved based
on a difference in absorption characteristics between bone such as the
ribs and soft tissue such as the heart. Radiation of different energies
is applied to the subject using two different image capturing conditions
to acquire two pieces of radiation image information. The extraction of
the bone or soft tissue of interest is achieved by computing the
difference between the two pieces of radiation image information with
predetermined weighting coefficients.

[0007]Since different internal structures of the subject have different
radiation absorption characteristics, it is necessary to process the
image in accordance with these characteristics to acquire a proper image
of the region of interest.

[0008]Japanese Laid-Open Patent Publications Nos. 2003-037778 and
2003-244542 disclose image processing method in which the extraction of
bone or soft tissue is achieved using a predetermined relation between
radiation source tube voltages, which determine the radiation dose to the
subject, and weighting coefficients used for computing a difference
between the pieces of radiation image information. The image processing
method disclosed in Japanese Laid-Open Patent Publication No.
2002-330954, acquires a first piece of radiation image information by
applying radiation to a subject in accordance with a predetermined image
capturing condition. Then, the image capturing condition is modified
based on analysis of the first piece of radiation image information, and
used for acquisition of a second piece of radiation image information.
Finally, an image of a region of interest is produced from the first and
second pieces of radiation image information.

[0009]The methods disclosed in Japanese Laid-Open Patent Publications Nos.
2003-037778 and 2003-244542, however, require highly experienced
operators for the determination of a suitable tube voltage and weighting
coefficient for a region of interest. Further, the above-mentioned
Publications are only concerned with the tissue of a subject, and no
consideration is given to methods for extraction or removal of a foreign
body within a subject. The method disclosed in Japanese Laid-Open Patent
Publication No. 2002-330954, which determines the image capturing
condition for the second piece of radiation image information based on
the first piece of radiation image information, may fail to obtain proper
image information when the subject moves before the acquisition of the
second piece of radiation image information.

SUMMARY OF THE INVENTION

[0010]It is a general object of the invention to provide a radiation image
processing apparatus and processing method for easily and reliably
extracting and removing a desired specific object in a subject from
radiation image information.

[0011]It is a main object of the invention to provide a radiation image
processing apparatus and processing method that allow acquisition of
radiation image information of a desired specific object without being
highly experienced in image processing.

[0012]It is another object of the invention to provide a radiation image
processing apparatus and processing method that allow acquisition of
radiation image information of a desired specific object in a subject
quickly and with high accuracy.

[0013]The above and other objects, features, and advantages of the present
invention will become more apparent from the following description when
taken in conjunction with the accompanying drawings in which a preferred
embodiment of the present invention is shown by way of illustrative
example.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a block diagram illustrating a configuration of a
radiation image processing apparatus according to an embodiment of the
invention;

[0016]FIG. 3 is a block diagram illustrating a circuit configuration of a
radiation detector according to an embodiment of the invention; and

[0017]FIG. 4 is a flowchart illustrating the operation of the radiation
image processing apparatus of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018]FIG. 1 is a block diagram illustrating a configuration of a
radiation image processing apparatus 10 according to an embodiment of the
present invention.

[0019]The radiation image processing apparatus 10 includes a radiation
source 14 for applying radiation X to a subject 12, a radiation source
controller 16 for controlling the radiation source 14 in accordance with
predetermined image capturing conditions such as a tube voltage, a tube
current, and irradiation time, and a solid-state radiation detector 18
(radiation converting panel) for converting the radiation X that has
passed through the subject 12 into charge information that serves as
radiation image information. The radiation image processing apparatus 10
further includes an image processor 20 for processing the radiation image
information detected by the solid-state radiation detector 18, a
processing condition memory 24 for storing processing conditions
including the above-mentioned image capturing conditions in the form of a
processing condition table shown in FIG. 2, and a processing condition
selector 26 for retrieving from the processing condition memory 24 a
processing condition required for producing desired radiation image
information. The radiation image processing apparatus 10 also includes a
display unit 28 for displaying the radiation image information processed
by the image processor 20, and a display controller 30 for controlling
the display unit 28.

[0020]The image processor 20 performs extraction or removal of a specific
object within the subject 12 from a radiation image by carrying out
weighted subtraction using a plurality of pieces of radiation image
information obtained at different radiation energies. The weighted
subtraction is computed as

S=αS1+S2

where S is a resultant piece of radiation image information, S1 and
S2 are pieces of radiation image information obtained with first and
second image capturing conditions, respectively, and α is a
weighting coefficient.

[0021]In order to obtain a resultant image having suitable contrast and
brightness after the extraction or removal of the specific object, the
weighted subtraction may alternatively be computed as

S=K1S1+K2S2+K3

where K1, K2 and K3 are coefficients determined by the
weight coefficient for extraction or removal of the specific object and
the gradation characteristics of the first and second pieces of radiation
image information S1 and S2.

[0022]FIG. 2 shows the processing condition table 22 stored in the
processing condition memory 24 of FIG. 1. In the present embodiment, the
processing condition table 22 includes a first image capturing condition
(S1), a second image capturing condition (S2), and a weighting
coefficient α, corresponding to a specific object and an image
capturing site. The first and second image capturing conditions (S1
and S2) and the weighting coefficient α are determined so as
to minimize exposure dose of the subject 12. Each of the first and second
image capturing conditions (S1 and S2) includes a tube voltage
and a tube current to be set to the radiation source 14. Processing
conditions A though D represent the condition required for extracting
soft tissue in a chest, the condition for extracting bone in a chest, the
condition for removing a plaster cast around a knee, and the condition
for removing a catheter inserted into a child's chest, respectively. Note
that the processing condition table 22 may also include other processing
conditions such as a condition for extraction or removal of an
internally-located foreign body, which may be made of glass, plastic,
metal, or the like. Such a condition may be determined based on the
radiation absorption characteristics of the material of the foreign body.
Note that the first and second image capturing conditions (S1 and
S2) may remain constant for all processing conditions, while the
weighting coefficient α varies with the specific object and the
image capturing site. On the other hand, a fixed weighting coefficient
α may be used for all processing conditions, while varying the
first and second image capturing conditions (S1 and S2) with
the specific object and the image capturing site.

[0023]FIG. 3 is a block diagram illustrating a circuit configuration of
the solid-state radiation detector 18. The solid-state radiation detector
18 includes a sensor substrate 38, a gate line driving circuit 44, a
signal reading circuit 46, and a timing control circuit 48 that controls
the gate line driving circuit 44 and the signal reading circuit 46.

[0024]The sensor substrate 38 includes a two-dimensional array of Thin
Film Transistors (TFTs) 52 and a photoelectric conversion layer 51
disposed over the TFTs 52. The photoelectric conversion layer 51 is made
of a material such as amorphous selenium (a-Se), which generates charge
on sensing radiation X. The sensor substrate 38 stores the charge
generated by the a-Se layer into storage capacitors 53. Then, the TFTs 52
in each row of the two-dimensional array are sequentially switched on to
allow the charge of the storage capacitors 53 to be read out as image
signals. FIG. 3 only shows the connection between one TFT 52 and one
pixel 50 which is made up of one storage capacitor 53 and a corresponding
part of the photoelectric conversion layer 51. The details of other
pixels 50 are omitted for clarity. Note that the amorphous selenium shows
performance degradation at high temperatures because of an inherent
structural change, and the amorphous selenium must therefore be used
within a predetermined temperature range. The TFT 52 of each pixel 50 is
connected to a gate line 54 extending in the row direction of the TFT
array and a signal line 56 extending in the column direction of the TFT
array. Each gate line 54 is connected to the gate line driving circuit
44, and each signal line 56 is connected to the signal reading circuit
46.

[0025]The radiation image processing apparatus 10 according to the
embodiment of the present invention is essentially configured as
described above. Now, the operation of the radiation image processing
apparatus 10 will be described with reference to the flowchart shown in
FIG. 4.

[0026]First, an operator selects one of the processing conditions stored
in the processing condition memory 24 using the processing condition
selector 26 (step S1). If, for example, radiation image information of
soft tissue of the chest of the subject 12 is desired, the processing
condition A is selected from the processing condition table 22 of the
processing condition memory 24.

[0027]Next, the first and second image capturing conditions (S1 and
S2) of the selected processing condition are provided to the
radiation source controller 16 (step S2).

[0028]A first shot is then captured by applying radiation X to the subject
12 with the radiation source controller 16 controlling the tube voltage
and the tube current of the radiation source 14 in accordance with the
first image capturing condition (S1) (step S3).

[0029]The radiation X that has passed through the subject 12 is converted
into an electric signal by the photoelectric conversion layer 51 of the
pixels 50 which make up the sensor substrate 38 of the solid-state
radiation detector 18. The electric signal is then stored into the
storage capacitor 53 as charge. Then, the timing control circuit 48
supplies timing control signals to the gate line driving circuit 44 and
the signal reading circuit 46 to allow readout from each storage
capacitor 53 of the charge information representing the first shot
radiation image information S1 of the subject 12.

[0030]More specifically, the gate line driving circuit 44 selects one of
the gate lines 54 in accordance with the timing control signal provided
by the timing control circuit 48 and supplies a driving signal to the
base terminal of each TFT 52 connected to the selected gate line 54.
Meanwhile, the signal reading circuit 46 selects the signal lines 56
connected to the charge detecting circuits 57 one after another in the
row direction of the TFT array in accordance with the timing control
signals provided from the timing control circuit 48. As a result, the
storage capacitor 53 of the pixel 50 corresponding to the selected gate
line 54 and signal line 56 discharges the charge information associated
with the piece of radiation image information S1, and the image
processor 20 receives this charge information as an image signal. After
the image signal from each of the pixels 50 arranged in the selected row
has been read out, the gate line driving circuit 44 selects the next gate
line 54 in the column direction and supplies the driving signal to the
selected gate line 54. The signal reading circuit 46 then reads out image
signals from the TFTs 52 connected to the selected gate line 54 in the
same manner. By repeating the operation described above, the
two-dimensional piece of radiation image information S1 stored in
the sensor substrate 38 is read out and provided to the image processor
20 (step S4).

[0031]Next, a second shot is captured by applying radiation X to the
subject 12 with the radiation source controller 16 controlling the tube
voltage and tube current of the radiation source 14 in accordance with
the second image capturing condition (S2) (step S5). It should be
noted that the second shot is performed immediately after the first shot
by the use of the predetermined second image capturing condition
(S2). Therefore, motion artifacts caused by the movement of the
subject 12 between the first and second shots do not occur.

[0032]The second shot radiation image information S2 detected by the
solid-state radiation detector 18 is read out in the same manner as the
first shot radiation image information S1 and provided to the image
processor 20 (step S6). If the subject 12 has moved between the first and
second shots, the image processor 20 processes the supplied information
to correct the positional relation of the images associated with the
pieces of radiation image information S1 and S2 before
performing further processing.

[0033]Next, the weighting coefficient α specified in the processing
condition selected by the processing condition selector 26 from the
processing condition memory 24 is provided to the image processor 20
(step S7).

[0034]The image processor 20 then calculates in step S8 a piece of
radiation image information S from the pieces of radiation image
information S1 and S2 supplied by the solid-state radiation
detector 18 and the weighting coefficient α selected from the
processing condition memory 24 using

S=aS1+S2.

[0035]The resultant piece of radiation image information S is displayed on
the display unit 28 by the display controller 30 (step S9). The display
unit 28 shows a radiation image in which the specific object selected by
the processing condition selector 26 is extracted, or a radiation image
in which the specific object is removed. For example, it should be noted
that the image processor 20 may also be provided with a processing
condition for extraction of a foreign object, so that radiation image
information can be computed and displayed to facilitate identification of
the foreign object within the body of the subject 12.

[0036]It should be noted that the present invention is not limited to the
embodiment described above and various variations and modifications may
be made without departing from the scope of the invention.

[0037]For example, instead of the solid-state radiation detector 18 that
converts applied radiation X directly into charge information, a
radiation detector may be employed that converts radiation X into visible
light by means of a scintillator, and then converts the visible light
into charge information. Alternatively, an optical readout radiation
detector may be utilized. The optical readout radiation detector may
store radiation X as a latent image and allow the latent image to be read
out as charge information when scanned with reading light. Another
possibility is to employ a stimulable phosphor panel, which stores
radiation energy in a phosphor and emits stimulated light of an intensity
corresponding to the stored energy when irradiated with stimulating light
such as a laser beam.

Patent applications by Atsushi Fukuda, Tokyo JP

Patent applications by Kazuharu Ueta, Tokyo JP

Patent applications by Sadato Akahori, Odawara-Shi JP

Patent applications by Yasunori Ohta, Yokohama-Shi JP

Patent applications by FUJIFILM CORPORATION

Patent applications in class X-ray film analysis (e.g., radiography)

Patent applications in all subclasses X-ray film analysis (e.g., radiography)